A typical commercial airplane gas turbine engine includes a thrust reverser cowling nacelle. The nacelle structure consists of an inner and outer cowl joined with bifurcations. The engine fan airstream runs through the annular cavity between the two cowls. The inner cowl or wall covers the engine case, accessories, and ducting installed therein. Because the engine case is very hot, up to 1100 degrees F., the inside surface of the inner cowl, referred to as the thrust reverser inner wall, is exposed to high radiative energy.
Thrust reverser inner wall structures have generally been made with aluminum skin, an aluminum honeycomb core, and a layer of applied insulation on the hot surface adjacent to the engine case. This metallic thrust reverser inner wall has been effective in conducting heat away from the engine to the surface adjacent to the fan airstream. A metallic structure is heavy, resulting in a significant weight penalty. In addition, the aluminum is susceptible to corrosion damage.
To reduce the weight penalties and improve acoustic characteristics, the thrust reverser inner wall has been built with an aluminum honeycomb core sandwiched between carbon fiber layers. As a result of the carbon fibers adjacent to the aluminum core, the wall structure has been susceptible to galvanic corrosion, particularly in the presence of moisture. Such corrosion creates a potential for subsequent structural failure of the aluminum core that is not acceptable.
Accordingly, the present invention provides a thrust reverser inner wall structure that substantially reduces the weight penalty realized, avoids susceptibility to corrosion, maintains the strength of the wall, and maintains adequate thermal conductivity, thereby reducing the need for insulation.
In accordance with the subject invention, a thrust reverser wall is a sandwich structure with a top layer of epoxy impregnated perforated carbon fiber fabric, a non-metallic, composite honeycomb core, and a bottom layer of epoxy impregnated carbon fiber fabric without perforations.
The non-metallic honeycomb core is made with pitch (based) carbon fibers to achieve the necessary thermal conductivity. The wall""s high level of thermal conductivity is such that the engine heat is conveyed to the perforated carbon fiber top layer. Engine fan air passing over the top layer acts as a heat sink wherein enough heat is carried away from the engine to minimize the need for insulation on the engine side of the wall.
These advantages of the present invention will be more clearly understood from the detailed description of the preferred embodiment that follows taken in conjunction with the features shown in the attached drawings.